fix(workspace): ensure chat markdown readability on forced-dark surface

apps/web/src/index.css

@@ -116,6 +116,39 @@ html.workspace-viewport-lock body {
   color: var(--foreground);
 }
 
+/*
+ * The chat always renders on the light workspace surface
+ * (`bg-[#f2f0e7]`, near-black text), but the app forces the dark theme
+ * app-wide (`forcedTheme="dark"`). Streamdown's code/table/mermaid chrome and
+ * the rules below read theme tokens, which under `.dark` resolve to near-black
+ * values — producing unreadable dark-on-dark blocks. Re-declare the relevant
+ * tokens to warm-light values inside the markdown context so every token-driven
+ * chrome (headers, copy/download/fullscreen controls, table borders/cells,
+ * inline code) reads correctly on the light surface without touching the
+ * global theme or unrelated UI.
+ */
+.workspace-surface .chat-markdown {
+  --background: #ffffff;
+  --foreground: #232321;
+  --muted: #f4f4f2;
+  --muted-foreground: #69675f;
+  --card: #ffffff;
+  --card-foreground: #232321;
+  --popover: #ffffff;
+  --popover-foreground: #232321;
+  --secondary: #f4f4f2;
+  --secondary-foreground: #232321;
+  --accent: #efece4;
+  --accent-foreground: #232321;
+  --sidebar: #ffffff;
+  --sidebar-foreground: #232321;
+  --sidebar-accent: #f4f4f2;
+  --sidebar-accent-foreground: #232321;
+  --border: #e2e0d6;
+  --input: #e2e0d6;
+  --ring: #b6b7b4;
+}
+
 .workspace-surface .chat-markdown,
 .workspace-surface .chat-reasoning,
 .workspace-surface .thinking-line {
@@ -223,6 +256,16 @@ html.workspace-viewport-lock body {
   text-align: start;
 }
 
+/* Readable header band + zebra rows so tables stand out on the surface. */
+.chat-markdown thead th {
+  background: var(--muted);
+  font-weight: 600;
+}
+
+.chat-markdown tbody tr:nth-child(even) {
+  background: color-mix(in oklch, var(--muted) 55%, transparent);
+}
+
 @media (prefers-reduced-motion: reduce) {
   .chat-markdown *,
   .chat-message,

apps/web/src/lib/workspace/frontend-regressions.test.ts

@@ -59,4 +59,20 @@ describe("Workspace frontend regression contracts", () => {
     expect(messageRenderer).toContain("mermaid");
     expect(messageRenderer).toContain("plugins={streamdownPlugins}");
   });
+
+  test("keeps markdown readable on the forced-dark workspace surface", () => {
+    const styles = source("../../index.css");
+
+    // The workspace surface is light, but the app forces the dark theme, so
+    // the markdown context must re-declare the theme tokens streamdown and the
+    // table/code rules read from. Without these the dark tokens (~22-28%
+    // lightness) produce near-black text, borders, and backgrounds.
+    expect(styles).toContain(".workspace-surface .chat-markdown");
+    expect(styles).toContain("--muted: #f4f4f2");
+    expect(styles).toContain("--border: #e2e0d6");
+    expect(styles).toContain("--sidebar: #ffffff");
+    // Table headers and zebra rows must stand out on the surface.
+    expect(styles).toContain(".chat-markdown thead th");
+    expect(styles).toContain(".chat-markdown tbody tr:nth-child(even)");
+  });
 });